Added leveldb::Status::IsInvalidArgument() method.

All other Status::Code enum values have an Is**() method with the one
exception of InvalidArgument.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=97166441

include/leveldb/status.h

@@ -63,6 +63,9 @@ class Status {
   // Returns true iff the status indicates a NotSupportedError.
   bool IsNotSupportedError() const { return code() == kNotSupported; }
 
+  // Returns true iff the status indicates an InvalidArgument.
+  bool IsInvalidArgument() const { return code() == kInvalidArgument; }
+
   // Return a string representation of this status suitable for printing.
   // Returns the string "OK" for success.
   std::string ToString() const;